SYNOPSIS

DESCRIPTION

The dbus-launch command is used to start a session bus
instance of dbus-daemon from a shell script.
It would normally be called from a user's login
scripts. Unlike the daemon itself, dbus-launch exits, so
backticks or the $() construct can be used to read information from
dbus-launch.

With no arguments, dbus-launch will launch a session bus
instance and print the address and pid of that instance to standard
output.

You may specify a program to be run; in this case, dbus-launch
will launch a session bus instance, set the appropriate environment
variables so the specified program can find the bus, and then execute the
specified program, with the specified arguments. See below for
examples.

If you launch a program, dbus-launch will not print the
information about the new bus to standard output.

When dbus-launch prints bus information to standard output, by
default it is in a simple key-value pairs format. However, you may
request several alternate syntaxes using the --sh-syntax, --csh-syntax,
--binary-syntax, or
--auto-syntax options. Several of these cause dbus-launch to emit shell code
to set up the environment.

With the --auto-syntax option, dbus-launch looks at the value
of the SHELL environment variable to determine which shell syntax
should be used. If SHELL ends in "csh", then csh-compatible code is
emitted; otherwise Bourne shell code is emitted. Instead of passing
--auto-syntax, you may explicity specify a particular one by using
--sh-syntax for Bourne syntax, or --csh-syntax for csh syntax.
In scripts, it's more robust to avoid --auto-syntax and you hopefully
know which shell your script is written in.

Here is an example of how to use dbus-launch with an
sh-compatible shell to start the per-session bus daemon:

## test for an existing bus daemon, just to be safe
if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then
## if not found, launch a new one
eval `dbus-launch --sh-syntax --exit-with-session`
echo "D-Bus per-session daemon address is: $DBUS_SESSION_BUS_ADDRESS"
fi

You might run something like that in your login scripts.

Another way to use dbus-launch is to run your main session
program, like so:

dbus-launch gnome-session

The above would likely be appropriate for ~/.xsession or ~/.Xclients.

AUTOMATIC LAUNCHING

If DBUS_SESSION_BUS_ADDRESS is not set for a process that tries to use
D-Bus, by default the process will attempt to invoke dbus-launch with
the --autolaunch option to start up a new session bus or find the
existing bus address on the X display or in a file in
~/.dbus/session-bus/

Whenever an autolaunch occurs, the application that had to
start a new bus will be in its own little world; it can effectively
end up starting a whole new session if it tries to use a lot of
bus services. This can be suboptimal or even totally broken, depending
on the app and what it tries to do.

There are two common reasons for autolaunch. One is ssh to a remote
machine. The ideal fix for that would be forwarding of
DBUS_SESSION_BUS_ADDRESS in the same way that DISPLAY is forwarded.
In the meantime, you can edit the session.conf config file to
have your session bus listen on TCP, and manually set
DBUS_SESSION_BUS_ADDRESS, if you like.

The second common reason for autolaunch is an su to another user, and
display of X applications running as the second user on the display
belonging to the first user. Perhaps the ideal fix in this case
would be to allow the second user to connect to the session bus of the
first user, just as they can connect to the first user's display.
However, a mechanism for that has not been coded.

You can always avoid autolaunch by manually setting
DBUS_SESSION_BUS_ADDRESS. Autolaunch happens because the default
address if none is set is "autolaunch:", so if any other address is
set there will be no autolaunch. You can however include autolaunch in
an explicit session bus address as a fallback, for example
DBUS_SESSION_BUS_ADDRESS="something:,autolaunch:" - in that case if
the first address doesn't work, processes will autolaunch. (The bus
address variable contains a comma-separated list of addresses to try.)

The --autolaunch option is considered an internal implementation
detail of libdbus, and in fact there are plans to change it. There's
no real reason to use it outside of the libdbus implementation anyhow.

OPTIONS

The following options are supported:

--auto-syntax

Choose --csh-syntax or --sh-syntax based on the SHELL environment variable.

--binary-syntax
Write to stdout a nul-terminated bus address, then the bus PID as a
binary integer of size sizeof(pid_t), then the bus X window ID as a
binary integer of size sizeof(long). Integers are in the machine's
byte order, not network byte order or any other canonical byte order.

--config-file=FILENAME

Pass --config-file=FILENAME to the bus daemon, instead of passing it
the --session argument. See the man page for dbus-daemon

--csh-syntax

Emit csh compatible code to set up environment variables.

--exit-with-session

If this option is provided, a persistent "babysitter" process will be
created that watches stdin for HUP and tries to connect to the X
server. If this process gets a HUP on stdin or loses its X connection,
it kills the message bus daemon.

--autolaunch=MACHINEID

This option implies that dbus-launch should scan for a
previously-started session and reuse the values found there. If no
session is found, it will start a new session. The
--exit-with-session option is implied if --autolaunch is given.
This option is for the exclusive use of libdbus, you do not want to
use it manually. It may change in the future.